1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to chemical mechanical polishing and methods of performing the same.
2. Description of the Related Art
Conventional chemical mechanical planarization or polishing (xe2x80x9cCMPxe2x80x9d) processes involve the planarization of a surface of a wafer or workpiece through the use of an abrasive slurry and various rinses and solvents. Material removal from the workpiece surface is through a combination of abrasive action and chemical reaction. In many processes, a quantity of abrasive slurry is introduced onto a polish pad of the CMP tool and distributed across the surface thereof by means of centrifugal force. Thereafter, one or more wafers are brought into sliding contact with the polish pad for a select period of time.
Conventional slurries normally contain several components, such as one or more types of abrasive particles, a stabilizer that is designed to keep the abrasive particles from going into solution, and one or more oxidizing agents. As the CMP process is consumptive of various slurry constituents, particularly the oxidizer components, it is necessary to replenish the slurry mixture frequently. Sometimes, the need for replenishment stems from the propensity for one or more of the slurry constituents to decompose over time. Hydrogen peroxide as an oxidizer is an example of such a rapidly decomposing constituent. The need for frequent replenishment, of course, increases the overall cost of the CMP process and can lead to variations in the slurry composition used for, and therefore the polish rates of, successive wafers in a given lot or for successive lots. Oxidizing agents like hydrogen peroxide also frequently oxidize organic and metallic components of CMP tools such as tubing or metallic surfaces exposed to slurry.
As design rules shrink and wafer sizes increase, accurate control ofpolishuniformity is critical. Various mechanisms contribute to polish non-uniformity, such as variations in polish pad topography, slurry composition and incoming film profile. Conventional methods of achieving post-polish uniformity focus on adjusting polish rates spatially. This is done through manipulation the local force between the wafer and polishing pad using: (1) conditioning to thin the pad in high-removal regions; (2) air flow behind the pad to push xe2x80x9cupxe2x80x9d harder in low-removal regions; or (3) application of air pressure behind the wafer to push xe2x80x9cdownxe2x80x9d harder in low-removal regions. While all three of these methods can be effective at a macro scale across the surface of a wafer, the fact that they rely on mechanical schemes means there is little that may be done on a more local scale at various locations on the wafer surface.
Predictable polish time periods again ensure that the polished film is planarized according to recipe and that process variations between successive wafers are minimal. However, conventional CMP processes sometimes do not proceed according to specified time periods. Process aborts are a leading cause of such variations. The causes for aborts are legion and include machine malfunction and slurry composition deviations to name just a few. Regardless of the exact cause, an abort usually results in the termination of the mechanical rotation of the wafer, or polish pad, depending on the tool type. During a normal CMP run, a wafer is exposed to a slurry and polished on a CMP machine for a preselected time period or until some other preselected endpoint is reached. The slurry is allowed to dwell, if at all, on the wafer surfaces for only preselected and relatively short time periods. However, during an abort, the chemical activity associated with the CMP slurry may continue, resulting in a static etch of the surfaces of the wafer exposed to the slurry. This can result in unwanted and substantial etch attack of various structures on the wafer.
The present invention is directed to overcoming or reducing the effects of one or mom of the foregoing disadvantages.
In accordance with one aspect of the present invention, a method of processing is provided that includes contacting a semiconductor workpiece to a solution, electrochemically generating a chemical species in the solution, and polishing the semiconductor workpiece with the aid of the solution.
In accordance with another aspect of the present invention, a method of processing is provided that includes contacting a surface of a semiconductor workpiece to an aqueous solution, electrochemically generating a chemical species in the aqueous solution that is oxidative of the surface of the semiconductor workpiece, and polishing the surface of the semiconductor workpiece with the aid of the solution.
In accordance with another aspect of the present invention, a processing device is provided that includes a member for polishing a surface of a semiconductor workpiece with the aid of a solution, a working electrode in fluid communication with the solution, and a counter electrode in fluid communication with the solution. A potential source is coupled to the working electrode and the counter electrode for applying a potential difference between the working electrode and the counter electrode to electrochemically generate a chemical species in the solution to aid in the polishing of the surface of the semiconductor workpiece.
In accordance with another aspect of the present invention, a processing device is provided that includes a member for polishing a surface of a semiconductor workpiece with the aid of a solution. A plurality of electrochemical cells is provided. Each of the plurality of electrochemical cells has a working electrode, a counter electrode and a reference electrode in fluid communication with the solution, and a potential source coupled to the working electrode and the counter electrode for applying a potential difference between the working electrode and the counter electrode to electrochemically generate a chemical species in the solution to aid in the polishing of the surface of the semiconductor workpiece.
In accordance with another aspect of the present invention, a processing device is provided that includes a member for polishing a surface of a semiconductor workpiece with the aid of a solution and a plurality of working electrodes in fluid communication with the solution. A counter electrode and a reference electrode are provided in fluid communication with the solution. A plurality of potential sources is coupled to the working electrodes and the counter electrode for applying a potential difference between the working electrodes and the counter electrode to electrochemically generate a chemical species in the solution to aid in the polishing of the surface of the semiconductor workpiece.